Fasenra (benralizumab) is a brand-name injection that’s prescribed for severe eosinophilic asthma in certain adults and children. As with other drugs, Fasenra can cause side effects, such as a headache or sore throat.

Fasenra can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took Fasenra in clinical trials:

  • headache
  • sore throat (see “Side effect specifics” below)

Mild side effects can occur with Fasenra use. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to Fasenra’s prescribing information.

Mild side effects that have been reported with Fasenra include:

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you develop a side effect while taking Fasenra and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see “Side effect specifics” below.

Severe allergic reaction was the only serious side effect reported in clinical trials of Fasenra. For more information, you can refer to Fasenra’s prescribing information.

If you develop serious side effects while taking Fasenra, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.


For some people, Fasenra can cause an allergic reaction.

In general, symptoms of allergic reaction can be mild or serious. You can learn more about possible symptoms in this article.

Ways to manage

For mild allergic reaction symptoms, such as a mild rash, call your doctor right away. They may recommend treatments to help manage your symptoms. They’ll also let you know whether you should keep taking the medication.

For severe allergic reaction symptoms, such as dizziness, severe rash, throat or facial swelling, and difficulty breathing, call 911 or your local emergency number right away. These symptoms require immediate medical care because they can become life threatening. If you’ve had a serious allergic reaction to Fasenra, your doctor may recommend taking a different medication instead.

Fasenra may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

Can Fasenra cause cancer?

It’s not likely. Cancer is not a reported side effect of Fasenra. One study from 2020 looking at the safety of Fasenra and similar drugs reported that Fasenra was not found to increase the risk of cancer.

Talk with your doctor or pharmacist if you have questions about the risk of cancer and Fasenra.

How long do side effects of Fasenra last?

The most common side effects of Fasenra are headache and sore throat. These are typically mild and will likely go away within a few days as your body adjusts to the drug.

Rarely, Fasenra may cause a severe allergic reaction that can develop right after your injection or several days later. If you have symptoms, such as skin rash, itching, dizziness, trouble breathing, or swelling in the face, get medical attention right away. You can call 911 or a local emergency number.

Talk with your doctor if you have side effects of Fasenra that are bothersome or don’t go away.

Learn more about some of the side effects that Fasenra may cause. To find out how often side effects occurred in clinical trials, see the prescribing information for Fasenra.

Sore throat

Sore throat was a common side effect of Fasenra reported in clinical trials. A sore throat may make talking, eating, or swallowing painful. Symptoms of a sore throat may include:

  • pain in your throat that’s worse when talking or swallowing
  • a scratchy sensation in the throat

What you can do

A sore throat will typically go away on its own after a few days. If your sore throat is bothersome, you can try a throat lozenge that you suck on. A cold treat, such as popsicles, can sometimes help relieve pain. Avoiding spicy or acidic foods may also help.

If your sore throat doesn’t go away or becomes severe, talk with your doctor right away.

Injection site reaction

Injection site reaction was a less common side effect in clinical trials of Fasenra. This is a reaction around the area where you receive your injection. Symptoms may include:

  • pain
  • redness or discoloration
  • itching
  • raised rash
  • bruising

What you can do

Injection site reactions are typically mild and will go away on their own. To help decrease the risk of this side effect, be sure to take the injection pen out of the refrigerator and let it warm to room temperature for about 30 minutes before you inject your dose.

Also, make sure you are using the correct injection technique. Your doctor or pharmacist can show you the correct way to inject Fasenra. The manufacturer of Fasenra also has a video on its website with instructions for self-injecting the medication.

When injecting the medication, make sure to use a different spot on your arm, abdomen, or thigh for each dose. (Injections in the arm should only be given by a healthcare professional or caregiver. For more details, see this article.)

If you get an injection site reaction after your dose, applying a cold compress may help relieve itching, swelling, and pain.

Talk with your doctor if you experience injection site reactions that get swollen, painful, and warm to the touch.

Below is important information you should consider before taking Fasenra.

Other precautions

Before taking Fasenra, discuss your health history with your doctor. Fasenra may not be right for you if you have certain medical conditions or other factors affecting your health. Be sure to talk with your doctor if any of the following apply to you:

Disclaimer: Medical News Today has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.